Differential response of cyanobacteria to sevin (carbaryl, 50%) and endotaf (endosulfan, 35%) pesticides: A qualitative and quantitative assay
In the present research endeavor, a total of 19 cyanobacterial taxa appeared in the composite soils in the control flasks belonging to 14 genera and 06 families. Their taxonomical characterization was made by using standard literature following Desikachary after 30 days of incubation. Stock solutions of Sevin (carbaryl, 50%) and Endotaf (endosulfan, 35%) pesticides were freshly prepared and added to the BG-11 culture media to obtain the 100, 250, 500 and 1000 ppm concentrations. The occurrence of cyanobacteria remained almost unaffected even in the presence of Sevin pesticides at 100 ppm dose in the test soil. However, their quantitative occurrence was decreased to a considerable extent. With increase in the dose level, proportionate decrease in their occurrence was noted. At 500 ppm dose level, most of the unicellular and filamentous forms of the cyanobacteria could not grow in the test soils except the cyanobacterial species Gloeocapsa kuetzingiana, Lyngbya polysiphoniae, Scytonema subtile and Calothrix javanica. The effect of organochlorine pesticides, Endotaf on the occurrence of cyanobacterial forms were quite specific. These cyanobacterial species were almost completely eliminated from the soils in presence of 500 ppm concentration of Endotaf. Only Lyngbya polysiphoniae and Calothrix javanica tolerated upto 500 ppm of Rogor. However, few filaments of Lyngbya polysiphoniae appeared in the soils supplemented with 500 ppm of Endotaf. Further increase in pesticides concentration at 1000 ppm with Rogor and Endotaf none of the cyanobacterial species were able to grow. The obtained results showed that, the organochlorine pesticide Endotaf was more toxic than the carbamate, Sevin to the cyanobacteria. From the obtained results, it was also seen that with higher doses of pesticide application in the crop fields i.e. more than 100 ppm of Sevin and even at 100 ppm of Endotaf, qualitative and quantitative occurrence of heterocystous and non- heterocystous cyanobacteria decreased considerably.